The production of fish mince from fatty fish species such as horse mackerel has the potential to provide high nutritional value products with a good source of protein and a high content of omega-3 fatty acids. Unfortunately, omega-3 fatty acids are very sensitive to oxidative deterioration. This can lead to development of off flavours, generation of unhealthy compounds, texture changes and significant loss of the initial nutritional and functional properties of the product. In order to maintain and secure a high nutritional and sensory quality of fatty fish products, oxidative deterioration during processing and storage must be minimised.

The aim of the project was to investigate the possibilities of using underexploited fish species like horse mackerel, or trachurus trachurus, for the production of healthy, high quality fish minces which were stable towards oxidative deterioration during processing and storage. Therefore, the project focussed on the evaluation, understanding and then control of oxidative reactions during processing and storage of horse mackerel products.

The objective of the first part of the project was to evaluate oxidative reactions taking place in both the lipid and the protein fractions during processing and storage of fish mince and to identify critical steps triggering such oxidative reactions. In order to obtain fish products with qualitative and quantitative differences in their lipid and protein fractions, horse mackerel minces were produced through mimicking the washing steps in the surimi production. After subsequent washing steps four different products were obtained and stored for up to 96 hours at +5 degrees Celsius and for up to 6 weeks at -10 degrees Celsius. Oxidative degradation of the four different products was evaluated during storage. The results revealed that oxidation developed simultaneously in the lipid and protein fractions during the products' processing and storage; however, more studies were required to investigate to which extent these reactions were linked. Furthermore, depending on the lipid contents and initial oxidative status of the product, oxidative reactions developed differently in the four studies' products. Additional factors, such as the level of pro-oxidants and antioxidants also influenced the oxidation rate in the different products.

These results underlined the necessity to protect the lipid and protein fractions against oxidation during all processing steps of fatty fish, as well as during storage. As such, the next step of the project was to investigate antioxidant strategies in order to maintain the initial nutritional and healthy properties of the fish mince during processing and storage. The antioxidative effect of propyl gallate, caffeic acid and spermine was investigated during the production and storage of fatty fish products. Incorporation of antioxidants was performed in the washing water during the washing steps. Such a strategy was found to effectively prevent the development of lipid and protein oxidation during processing of the fish paste and, subsequently, during storage at 5 degrees Celsius. The most efficient antioxidants were propyl gallate and caffeic acid, which almost completely inhibited oxidation during the entire storage period of 96 hours, while spermine only reduced the development of oxidation to a lesser extent. Propyl gallate and caffeic acid protected both the protein and lipid fractions against oxidation and maintained a high nutritional value of the fatty fish products.

By focussing on the development of oxidation in both the lipid and the protein fractions, this project offered a new insight into oxidative reactions in fatty fish, especially in protein oxidation. The obtained results also provided relevant information for the production of fatty fish with respect to the type of antioxidant to use and at which concentration, in order to obtain a product with a good oxidative stability, which retained its full nutritional value.